1. Field of the Invention
The present invention relates to corrugated paper board manufacture and to the belts required by the machines used to manufacture that variety of paper board. More specifically, the present invention relates to the belts that may be used on the single-facer section of a corrugated board production line.
2. Description of the Prior Art
In the manufacture of corrugated paper board, a so-called core paper is heated by steam, which makes it more pliable, and is then fed into a nip formed between a pair of toothed rollers whose teeth mesh, thereby corrugating the core paper in a uniform, undulating pattern. Starch paste is subsequently applied to the crests of the corrugated core paper, which is then mated to a liner paper in a press nip. There, the corrugated core paper and liner paper are bonded together to form a completed sheet, which can then be further processed as desired.
In one machine used for this purpose in the prior art, the press nip is formed by one of the toothed or corrugating rolls and a pressure roll. In another machine of a more recent design, the press nip is extended in the running direction through the use of a belt instead of a pressure roll. The belt holds the corrugated core paper and liner paper together against the corrugating roll for a significant portion of its circumference.
The belt experiences severe operating conditions. Because heat is used to vaporize moisture in the core paper, the belt operates in a high-temperature environment and under high tension. Further, the belt continually runs against the teeth on the corrugating roll albeit with the sheet in between the belt and roll to develop the required bonding pressure between the core paper and the liner paper. Moreover, the belt must be flexible yet have lengthwise strength and widthwise rigidity sufficient to withstand wrinkling, which may cause the belt to drift undesirably from side to side.
Still further, the belt faces two opposing problems. Initially, it is necessary that the belt have a sufficient coefficient of friction that the liner paper can be drawn into the nip by the belt and attached to the core paper. As a result there have been several solutions proposed for increasing the coefficient of friction on the surface of the belt including coating the belt with resins, needling fibers into the belt, and a combination of both of these procedures, as discussed in commonly assigned U.S. Pat. Nos. 6,470,944 and 6,276,420, both of which are incorporated herein by reference. Although both of these solutions increase the coefficient of friction sufficient to enable the belt to draw the liner paper into the nip, in certain instances they may create an opposing problem as the paper exits the nip in that the coefficient of friction can be so great that the bonded core and liner papers are drawn in the direction of travel of the belt. This results in decreased quality of the corrugated board. Accordingly, there is a need for a corrugator belt that has the ability to adequately vent moisture from the board, release the board cleanly after the nip, and has a sufficiently high coefficient of friction that the liner paper can be drawn into the nip.
The present invention provides an improvement and/or solution to the problems inherent in the use of a belt of the foregoing varieties.